The cormous genus Gladiolus is probably second only to the genus Iris in size within the Iridaceae. There are about 8 to 10 small, fairly hardy species from Europe and western Asia. However, the genus is most highly developed in Africa, where there are over 245 known species.
The Eurasian Gladiolus are all pink to mauve to light rose-purple in color. The hardiest for cold climates seems to be Gladiolus imbricatus, whose seeds and dormant corms require a period of chilling in order to grow. Commoner in garden catalogs is Gladiolus communis byzantinus, which blooms very early in Spring. G. byzantinus is not as hardy as imbricatus, so plant a large number of corms of byzantinus (two or more dozen). The survivors will continue to be hardy in your garden.
Other Eurasian species in cultivation include Gladiolus illyricus and G. italicus.
Most of the African Gladiolus are rather tender, as are most of the garden hybrids derived from them over the years. In cold climates, they perform best in the garden when the corms are planted outdoors in the garden in spring and are dug in the autumn. They should be stored indoors over winter.
Gladiolus x-gandavensis is a hardy hybrid developed from South African species, such as G. dalenii. It is often confused with Gladiolus dalenii primulinus, which seems to be a different plant. G. x-gandavensis blooms in late summer or early autumn.
Another potentially cold-hardy Gladiolus is G. oppositiflorus salmoneus, which occurs in the high Drakensberg of South Africa. This species is currently (2002) being tested for cold hardiness here at Shields Gardens Ltd., where it blooms in late summer or early autumn.